1. Technical Field
The present invention relates to a positioning method, a program of the positioning method, and a positioning device.
2. Related Art
The global positioning system (GPS) is widely known as a positioning system utilizing a positioning signal. The GPS is utilized for a position calculation device provided in a portable telephone, a car navigation system, and the like. A GPS receiver locates its current position by calculating four parameters (i.e., three-dimensional coordinate values that indicate the position of the GPS receiver and a clock error) based on information such as the positions of a plurality of GPS satellites and the pseudo-range between each GPS satellite and the GPS receiver (i.e., positioning calculations).
The GPS satellite signal transmitted form the GPS satellite is modulated with a spread code called a PRN code unique to each GPS satellite. Further, it is known that the polarity of the PRN code can be reversed at a 20 millisecond interval by the phase modulation with the navigation data (see e.g., JP-A-11-258326).
In a positioning device of the related art, in order to capture (extract) the GPS satellite signal in a faint received signal, there is generally used a method of cumulatively adding (accumulating) the received signal for a predetermined cumulative addition period, and calculating correlation with a replica code of the PRN code on the signal resulted from the cumulative addition.
However, as described above, the timing at which the polarity of the PRN code is reversed (hereinafter referred to as a “polarity reversal timing”) can appear at every 20 millisecond interval (hereinafter referred to as “polarity reversible timing”). Therefore, in the case in which the cumulative addition (cumulative calculation) is executed over a polarity reversible timing and the polarity is reversed at the polarity reversible timing, it may well occur that a signal with different polarities is cumulatively added before and after the timing. If the signal with different polarities is cumulatively added, a part or the whole of the received signal is canceled, which causes a problem of degradation in the receiver sensitivity.